The padlock has been replaced by the site identity button, for details on using it see https://support.mozilla.com/kb/Site+Identity+Button

If you want to add a padlock icon to the location bar, you can use the Padlock add-on - https://addons.mozilla.org/firefox/addon/padlock-icon/

Thank you.

Please click the Solved It button next to the answer that solved your Firefox support issue, it appears when you are logged in, so this thread gets marked as Solved to help other users who may have this same problem.

TonyE, thanks for your help on this issue.